1. Field of the Invention
This invention relates to the preparation of slurry metal catalysts useful in Fischer-Tropsch synthesis by the in situ decomposition of Group VIII metal carbonyls in the presence of hydrothermally stable metal oxides.
2. Brief Description of the Prior Art
A number of catalyst systems have been prepared by in situ decomposition of various Group VIII metal carbonyl complexes, alone or in the presence of various support materials, i.e., H. Schultz in New Synthesis with Carbon Monoxide, J. Falbe, Ed., Springer Verlag, Berline (1980).
However, these studies have failed to establish or identify the effects and ultimate influence of the support on catalyst properties. They have frequently employed rather severe conditions, i.e., elevated temperatures and/or pressures to achieve the required carbonyl decomposition step. These conditions can, in many cases, adversely affect catalyst performance due to undesired sintering, agglomeration or deposition of the metal on the support material in an uncontrolled way.
McVicker and Vannice described the production of potassium Group VII metal Fischer-Tropsch catalysts by impregnation of Al.sub.2 O.sub.3 or SiO.sub.2 with potassium Group VIII metal carbonyl complexes in J. Catalysis, 63, 25 (1980). Their catalysts were prepared ex situ with a high temperature (350.degree. C.) vacuum drying, followed by a 500.degree. C. H.sub.2 treatment to activate the material.
Smith and coworkers in J. Amer. Chem. Soc. 100, 2590 (1978) have described a procedure for production of supported Group VIII metal catalysts by decomposition of metal carbonyl complexes on Al.sub.2 O.sub.3. They indicated that these catalysts are active for conversion of CO/H.sub.2 to methane and that if the carbonyl decomposition step was performed in a CO/H.sub.2 containing gas that methane was formed.
Tatsumi and coworkers recently reported that zeolite entrapped ruthenium carbonyl clusters are active for Fischer-Tropsch synthesis, J. C. S. Chem. Comm., page 207 (1985). Their catalysts were prepared by ex-situ procedures involving vacuum drying of the zeolite at 400.degree. C., impregnation at 120.degree. C., followed by activation at 200.degree. C. in H.sub.2 or N.sub.2. Their catalyst when tested with a 1:1 H.sub.2 :CO feed generated a Fischer-Tropsch product mixture rich in C.sub.1 -C.sub.4 hydrocarbons.
Madon has recently disclosed, in U.S. Pat. No. 4,477,595, the use of supported ruthenium catalysts for the production of liquid hydrocarbons from CO/H.sub.2. The catalysts useful in this process were prepared from RuCl.sub.3 or Ru(NO.sub.3).sub.3 and were activated at 400.degree.-450.degree. C. in flowing H.sub.2 before use.
In none of the above examples is there described a procedure for generating an active supported ruthenium catalyst for the selective synthesis of liquid hydrocarbons under slurry reactor conditions.
F. Bellstedt, in Dissertation, Karlsruhe (1971), has described the preparation of slurried ruthenium catalysts by in situ decomposition of Ru.sub.3 CO.sub.12 at 100.degree. to 150.degree. C. and 50 to 100 bar. Supports such as kieselguhr, active carbon, aluminum oxide and ruthenium (IV) oxide were employed.
However, we have successfully attempted to prepare an analogous active catalyst via decomposition of Ru.sub.3 CO.sub.12 at 200.degree. to 220.degree. C. and 1 to 2 bar H.sub.2. The catalyst exhibited only marginal CO hydrogenation activity over a 16-hour operating period. In addition, the reaction mixture which was discharged from the reactor contained detectable quantities of the precursor complex, Ru.sub.3 CO.sub.12, indicating that the decomposition step did not proceed to complete conversion.